1. Field of the Invention
This invention relates to the control of a telephone call received from a third person during a telephone call.
2. Description of the Related Art
In a key telephone system, a key telephone set is assigned a main extension number and a pseudo extension number. Here, the pseudo extension number is the number assigned to the main extension without a physical accommodation position and a key telephone set. For example, the main extension number of No. 200 is assigned to a key telephone set, as well as the pseudo extension numbers such as No. 500 and No. 501. These the pseudo extension numbers are also assigned to other key telephone sets. Although the user of this key telephone set can usually talk over the telephone by using the main extension number of No. 200, he can also talk over the telephone by using the pseudo extension numbers of No. 500 or No. 501.
Next, the call process using the main extension number of a conventional key telephone system is explained. If a telephone call to the main extension number is received in the key telephone system, the destination of the telephone call is determined by analyzing the telephone call based on the extension number. Next, the key telephone system judges whether the key telephone set of the main extension number is busy by using the extension number. If the key telephone set of this main extension number is not busy, a ring-back tone is sent to the caller. On the other hand, if the key telephone set of the main extension number is busy, a busy tone is sent to the caller. Therefore, when the main extension No. 200 on the key telephone set is busy, and a telephone call to that extension is received from an other caller, a busy tone is sent to that caller.
The caller then knows that the key telephone set, which is the destination, is busy, and will hang up the telephone.
On the other hand, if a telephone call to the main extension number is received from an other caller when the key telephone set is utilizing one of the pseudo-extensions, for example pseudo extension number of No. 500, the key telephone system judges that the key telephone set is not busy because the extension of No. 200 is idle. The key telephone system thus makes the key telephone set ring.
However, because the key telephone set is busy through use of the pseudo extension number No. 500 at this time, the user of the key telephone set cannot answer the telephone call coming in on main extension number No. 200. The key telephone set thus continues to ring. For this reason, the user of the key telephone set cannot continue the telephone call on the pseudo extension number calmly. Moreover, since the caller does not understand that the key telephone set is busy, he wastes time waiting for someone to answer the phone.